Recently, Liquid Crystal Display (LCD hereinafter) that has the characteristics of being thin and high definition, and Electro Luminescent Display (ELD hereinafter) that uses organic electro-luminescence element have been widely used. The former, the LCD generally has a lighting device called backlight or frontlight, and displays a picture by transmitting or reflecting the light from these light. In order to keep the display screen of such a device easy to see or power consumption low, the idea of automatically adjusting the light quantity of backlight and frontlight according to the ambient brightness has been suggested.
FIG. 9 is a block diagram showing the function structure of an LCD described in Patent Document 1. In FIG. 9, 100 is an optical sensor that detects the external brightness of the device, 101 is a backlight, the light source of the device, 102 is a luminance adjusting unit that adjusts the luminance of the backlight, 103 is a memory that stores the data used for adjusting the luminance, and 104 is a processing unit that transmits a signal used for adjusting the luminance to the luminance adjusting unit 102, based on the signal from the optical sensor 100 and the data of the memory 103. This LCD stores the information of the backlight luminance that corresponds to the preset quantity of light received by the device in the memory 103, lets the processing unit 104 calculate a luminance value of the backlight 101 that corresponds to the quantity of light received by the optical sensor 100 based on the data in the memory 103, and lets the luminance adjusting unit 102 automatically adjust the luminance of the backlight 101 based on the result of the calculation by the processing unit 104. The same kinds of technologies are described in Patent Documents 2 and 3. What is common among these devices is the fact that they all require a separate optical sensor near the display device. Because of this, the device tends to be large, there are restrictions as to where the optical sensor should be placed, and accurate light control cannot be achieved since the brightness is not measured directly at the display section.
FIG. 10 is a drawing showing the structure of an LCD described in Patent Document 4. In FIG. 10, 110 is a liquid crystal display panel, 111 is an optical sensor formed on the substrate whereon a thin film transistor (TFT hereinafter) of the liquid crystal display panel is formed, 112 is a backlight, the light source of the liquid crystal display panel, 113 is a control circuit that controls the luminance of the backlight 112 according to a signal from the optical sensor 111. In this method, the optical sensor 111 is formed on the substrate that comprises the liquid crystal display panel 110. Therefore, it is not necessary to provide a separate optical sensor externally, and the problems mentioned above such as the increase in size and the layout restrictions stemming from the shape of the device do not occur. Further, since the optical sensor can be placed very close to the display section, the brightness of the display section can be measured accurately. Patent Documents 5 and 6 describe the same kind of technologies.    [Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-04-352128    [Patent Document 2]
Japanese Patent Kokai Publication No. JP-A-61-259287    [Patent Document 3]
Japanese Patent Kokai Publication No. JP-A-02-309316    [Patent Document 4]
Japanese Patent Kokai Publication No. JP-A-06-11690    [Patent Document 5]
Japanese Patent Kokai Publication No. JP-A-64-006927    [Patent Document 6]
Japanese Patent Kokai Publication No. JP-A-03-249622